1. Field of the Invention
This invention concerns discharge lamp lighting device. In particular, it concerns a lighting device made up of a very high pressure discharge lamp that contains at least 0.20 mg/mm3 of mercury and operates at a pressure of at least 200 atmospheres, and a power supply device.
2. Description of Related Art
Projector equipment is generally of the type that uses liquid crystal panels and the type that uses DLP®. The method that uses liquid crystal panels has both a one-chip variety and a three-chip variety, but with either variety, the beam emitted from the light source is split into three colors (RGB), and after transmission coordination of the light corresponding to image information in the liquid crystal panel, the three colors that pass through the panels are combined and projected onto a screen.
In the type that uses DLP®, on the other hand, the beam emitted from the light source passes through a rotating filter by which the RGB domains are divided and formed, irradiated by means of time division, such as a space modulation element (what is called a light modulation device, or specifically a DMD (digital micromirror device) element), and specified beams are reflected by the DMD element and projected onto the screen. A DMD element is spread with several million small mirrors, one per pixel, and by controlling the direction of each small mirror, it is possible to control the projection of light.
In comparison with the liquid crystal method, the DLP® method has a simpler optical system and there is no need to use as many as three layers of liquid crystal panel, so that the equipment, as a whole, has the advantage of being smaller and simpler.
High pressure discharge lamps with high mercury vapor pressure are used as light sources for projection equipment. The reason for the high mercury vapor pressure is to enable a high light output in the visible spectrum.
Further, it is know that when high mercury vapor pressure discharge lamps of this sort are operated, projections are formed at the tips of the electrodes. There are also cases where the projections are not formed during operation, electrodes being used on which projections have been formed in advance on the tips of a massive portion at the tip of each electrode by means of cutting or fusing. Whether they are formed during operation or created in advance, these projections have the purpose of stabilizing the arc spot and preventing flicker; they are indispensable for light sources of projector equipment.
On the other hand, projector equipment is expected to project an image as quickly as possible after start-up, and so light sources in which the luminous flux rises in a short time after the beginning of discharge are preferred. The best known method to hasten the rise of luminous flux is provide, from the beginning of discharge, current that exceeds the current value during steady state operation.
In the case of discharge lamps that have projections on the tips of the electrodes, however, there is the problem that providing a large current immediately after the beginning of discharge will melt or deform the projections. Examples of discharge lamps that have projections on the tips of their electrodes can be found in JP-A-2002-245965 that corresponds to U.S. Pat. No. 6,552,449 and JP-A-2004-296427 that corresponds to U.S. Pat. No. 7,122,960.